Grids tie together distributed storage systems and execution platforms into globally accessible resources. Data Grids provide collection management and global namespaces for organizing data objects that reside within a grid. Knowledge-based grids provide concept spaces for discovering relevant data objects. In a knowledge-based grid, data objects are discovered by mapping from scientific domain concepts, to the attributes used within a data grid collection, to the digital objects residing in an archival storage system. These concepts will be explored in the context of large-scale storage in the web, and illustrated based on infrastructure under development at the San Diego Supercomputer Center.